mc-server on-demand sysinfo via bundled minefetch watcher

mc-server

Tightened how the server pulls host stats from the minefetch companion.

changes

• Read the minefetch location from the MC_MINEFETCH_DIR environment variable instead of a hardcoded path.
• Bundle the sysinfo watcher from the minefetch repo and use a Minefetch-specific fastfetch config.
• On-demand sysinfo refresh via a host-side watcher driving fastfetch.